Adaptationism
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Adaptationism is a scientific perspective on evolution that focuses on accounting for the products of evolution as collections of adaptive traits, each a product of natural selection with some adaptive rationale or raison d'etre.[1][2] [3] [4] A formal alternative would be to look at the products of evolution as the result of neutral evolution, in terms of structural constraints, or in terms of a mixture of factors including (but not limited to) natural selection.[4]
The most obvious justification for an adaptationist perspective is the belief that traits are, in fact, always adaptations built by natural selection for their functional role. This position is called "empirical adaptationism" by Godfrey-Smith.[5] However, Godfrey-Smith also identifies "methodological" and "explanatory" flavors of adaptationism, and argues that all 3 are found in the evolutionary literature (see [1] for explanation).
Although adaptationism has always existed— the view that the features of organisms are wonderfully adapted predates evolutionary thinking— and was sometimes criticized for its "Panglossian" excesses (e.g., by Bateson or Haldane), concerns about the role of adaptationism in scientific research did not become a major issue of debate until evolutionary biologists Stephen Jay Gould and Richard Lewontin penned a famous critique, "The Spandrels of San Marco and the Panglossian Paradigm". [6] According to Gould and Lewontin, evolutionary biologists had a habit of proposing adaptive explanations for any trait by default without considering non-adaptive alternatives, and often by conflating products of adaptation with the process of
This critique provoked defenses by Mayr,[2] Reeve and Sherman [3] and others, who argued that the adaptationist research program was unquestionably highly successful, and that the causal and methodological basis for considering alternatives was weak. The "Spandrels paper" (as it came to be known) also added fuel to the emergence of an alternative "evo-devo" agenda focused on developmental "constraints" [7] Today, molecular evolutionists often cite neutral evolution as the null hypothesis in evolutionary studies, i.e., offering a direct contrast to the adaptationist approach.[8][9] Constructive neutral evolution has been suggested as a means by which complex systems emerge through neutral transitions, and has been invoked to help understand the origins of a wide variety of features from the spliceosome of eukaryotes to the interdependency and simplification widespread in microbial communities.[10][11]
Introduction
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Criteria to identify a trait as an adaptation
Adaptationism is an approach to studying the evolution of form and function. It attempts to frame the existence and persistence of traits, assuming that each of them arose independently and improved the reproductive success of the organism's ancestors. A trait is an adaptation if it fulfils the following criteria:
- The trait is a variation of an earlier form.
- The trait is heritable through the transmission of genes.
- The trait enhances reproductive success.
Constraints on the power of evolution
Genetic constraints
Genetic reality provides constraints on the power of random mutation followed by natural selection.
With pleiotropy, some genes control multiple traits, so that adaptation of one trait is impeded by effects on other traits that are not necessarily adaptive. Selection that influences epistasis is a case where the regulation or expression of one gene, depends on one or several others. This is true for a good number of genes though to differing extents. The reason why this leads to muddied responses is that selection for a trait that is epistatically based can mean that an allele for a gene that is epistatic when selected would happen to affect others. This leads to the coregulation of others for a reason other than there is an adaptive quality to each of those traits. Like with pleiotropy, traits could reach fixation in a population as a by-product of selection for another.
In the context of development the difference between pleiotropy and epistasis is not so clear but at the genetic level the distinction is more clear. With these traits as being by-products of others it can ultimately be said that these traits evolved but not that they necessarily represent adaptations.
Anatomical constraints
Anatomical constraints are features of organism's anatomy that are prevented from change by being constrained in some way. When organisms diverge from a common ancestor and inherit certain characteristics which become modified by natural selection of mutant phenotypes, it is as if some traits are locked in place and are unable to change in certain ways. Some textbook anatomical constraints often include examples of structures that connect parts of the body together though a physical link.
These links are hard if not impossible to break because evolution usually requires that anatomy be formed by small consecutive modifications in populations through generations. In his book, Why We Get Sick,
Another example is the
Debate with structuralism
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Adaptationism is sometimes characterized by critics as an unsubstantiated assumption that all or most traits are
Adaptationist researchers respond by asserting that they, too, follow
Purpose and function
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There are philosophical issues with the way biologists speak of function, effectively invoking teleology, the purpose of an adaptation.
Function
To say something has a function is to say something about what it does for the organism. It also says something about its history: how it has come about. A heart pumps blood: that is its function. It also emits sound, which is considered to be an ancillary side-effect, not its function. The heart has a history (which may be well or poorly understood), and that history is about how natural selection formed and maintained the heart as a pump. Every aspect of an organism that has a function has a history. Now, an adaptation must have a functional history: therefore we expect it must have undergone selection caused by relative survival in its habitat. It would be quite wrong to use the word adaptation about a trait which arose as a by-product.[13][14][verification needed]
Teleology
See also
- Adaptive evolution in the human genome
- Beneficial acclimation hypothesis
- Constructive neutral evolution
- Evolutionary failure
- Exaptation
- Gene-centered view of evolution
- Neutral theory of molecular evolution
- Vitalism
References
- ^ a b S. H. Orzack and P. Forber (2017). "Adaptationism". In E. N. Zalta (ed.). The Stanford Encyclopedia of Philosophy.
- ^ doi:10.1086/284064.
- ^ doi:10.1086/417909.
- ^ .
- ISBN 978-0-521-59166-9.
- ^ S. J. Gould and R. C. Lewontin (1979). "The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist program". Proc. Royal Soc. London B. 205: 581–598.
- ^ R. Amundson (2005). The Changing Role of the Embryo in Evolution. Cambridge University Press, Cambridge, UK.
- PMID 28010725.
- ^ L. Duret (2008). "Neutral theory: The null hypothesis of molecular evolution". Nature Education. 1: 218.
- S2CID 7306575.
- S2CID 90290787.
- Richard C. Lewontin. "The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme" Proc. R. Soc. London B 205 (1979) pp. 581–598
- ^ Sober 1993, pp. 85–86
- ^ Williams 1966, pp. 8–10
- JSTOR 2025745. Teleology Revisisted: The Dewy Lectures 1977 (first lecture)
- JSTOR 2025746. Teleology Revisisted: The Dewy Lectures 1977 (second lecture)
- ^ Mayr 1965, pp. 33–50
- ^ Mayr 1988, Ch. 3, "The Multiple Meanings of Teleological"
- ^ Williams 1966, Ch. 9, "The Scientific Study of Adaptation"
- OCLC 444678726. Retrieved 2015-08-24.
- ^ Hull 1982, p. 298
Sources
- Cronin, H. (1992). The Ant and the Peacock: Altruism and Sexual Selection from Darwin to Today. Cambridge: Cambridge University Press. ISBN 978-0-521-32937-8.
- S2CID 2129408.
- OCLC 502399533.
- PMID 435219.
- ISBN 978-0-06-097519-7.
- ISBN 978-0-14-023013-0.
- OCLC 384895.
- OCLC 17108004.
- OCLC 209901.
- Orzack, S.H.; Sober, E.R., eds. (2001). Adaptationism and Optimality. Cambridge: Cambridge University Press. ISBN 978-0-521-59166-9.
- OCLC 191989.[page needed]
- Sober, E. (1998). "Six Sayings about Adaptationism". In D. Hull; M. Ruse (eds.). The Philosophy of Biology. Oxford: Oxford University Press. ISBN 978-0-19-875213-4.
- Sober, Elliott (1993). Philosophy of Biology. Dimensions of Philosophy Series. Boulder, CO: OCLC 26974492.
- OCLC 35230452.
External links
- Information from "Deep Ethology" course website, by Neil Greenberg
- Tooby & Cosmides comments on Maynard Smith's New York Review of Books piece on Gould et al.